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Chp-13

Dr. Syed Mohammed Ahmad ; Rehana Khan Laxmi Publications PDF

258

A BOOK

OF

BIOTECHNOLOGY

Chapt er

Chapter

13

TRACER TECHNIQUE—THE USE

OF ISOTOPES AS TRACERS

INTRODUCTION

The atoms of most chemical elements exist in more than one variety. Each kind of a given element has a different atomic weight, but all of them carry the same nuclear charge. For example, there are three different kinds of magnesium atoms with atomic weights of 24, 25, and 26 respectively. Such different varieties of atoms of a given element are called isotopes.

Differences in the chemical behaviour of two isotopes of the same element are so slight as to be barely detectable, and ordinarily they cannot be separated by chemical methods. The chemical properties of all isotopes of a given element are virtually identical, because all have the same electronic configuration ; one isotope differs from another only in the constitution of the atomic nucleus which is composed of protons and neutrons.

RADIOACTIVE ISOTOPES

In addition to the stable isotopes described above, there are many radioactive isotopes of certain heavy elements such as uranium and radium occur in nature. The atoms of many elements not normally radioactive may be made so by bombardment with various types of elementary particles such as neutrons, protons, deutrons, and alpha particles. Such bombardments are usually accomplished with the aid of a cyclotron or a uranium pile reactor.

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Chp-2

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A BOOK

OF

BIOTECHNOLOGY

Chapt er

Chapter

CHEMISTRY

FOR

2

BIOLOGISTS

INTRODUCTION

Chemistry is the science that deals with the composition and structure of matter and with the transformations that matter undergoes. Chemistry is a rather broad field; at one extreme, in theoretical chemistry and spectroscopy, it borders on physics, and at the other extreme, in organic chemistry, it borders on biochemistry and biology.

ATOMS, MOLECULES, ELEMENTS, COMPOUNDS

All substances, whether gas, liquid, or solid, have certain fundamental characteristics in common. If one could break down any substance into its smallest elemental units, it would be composed of atoms. Although it is difficult to observe atomic structure, atoms are known to consist of a mass of positively charged protons, noncharged (or neutral) neutrons, tiny negatively charged electrons, and other even smaller subparticles. An atom has equal numbers of electrons and protons; thus it has a total charge that is zero. When an atom loses or gains electrons it becomes a negatively or positively charged ion (e.g., Na+, Cl–). The protons and neutrons are found in a central nucleus, and the electons float around the nucleus, like negatively charged satellites attracted to a positively charged planet.

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Chp-1

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Chapt er

Chapter

1

MICROSCOPY

INTRODUCTION

Almost all cells are too small to be examined directly with the human eye and so, our knowledge of cells has depended very much on microscopic techniques for magnifying them.

The history of cell biology is an excellent example of the effect of one scientific discipline on another. The improvements in microscopy produced by developments in physics have been closely correlated with the expansion of cell biology. It is interesting to compare the appearance of the microscope used by Robert Hook in the seventeenth century with that of modern light and electron microscope. The magnifications attainable by these microscopes range from X 100 to X 400,000. In addition, several different kinds of microscopy are available, and many techniques have been developed by means of which specimens can be prepared for examination.

Each type of microscopy and each method of preparing specimens for examination offers advantages for demonstration of specific morphological features.

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Chp-10

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A BOOK

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BIOTECHNOLOGY

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Chapter

10

CARBOHYDRATES

INTRODUCTION

Carbohydrates are a group of organic compounds containing the elements carbon, hydrogen, and oxygen, generally in the ratio of 1 : 2 : 1, with the general formula (CH2O)n (the n in the formula means that CH2O is repeated a certain number of times ; if 6 times, a molecule of glucose –C6H12O6 is formed.) One carbon bears a carbonyl group and the others hydroxyl groups. However, the definition of this group (as hydrates of carbon) has been broadened to include compounds containing nitrogen and sulphur, and compounds that do not conform to a strict 1 : 2 : 1 ratio of carbon, hydrogen, and oxygen. Carbohydrates, therefore, are considered to be polyhydroxy—aldehydes or polyhydroxy-ketones, and their derivatives.

The carbohydrates are derived more or less directly from carbon dioxide and water in photosynthesis. Sugar, starch, and cellulose are examples of carbohydrates that illustrate the importance of this class of compounds to life. Cellulose is the principal constituent of wood

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Chp-12

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A BOOK

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BIOTECHNOLOGY

Chapt er

Chapter

12

CHROMATOGRAPHY

INTRODUCTION

Chromatography is an analytical technique for separating two or more chemical compounds in solution by taking advantage of the fact that they are removed from solution at different rates when the latter is percolated down a column of a powdered adsorbent or passed across the surface of an absorbent paper. This is one of the most significant and reliable methods used in the fields of chemistry and biological sciences to obtain and identify substances (such as proteins, chlorophyll pigments, etc.), in a high state of purity.

Chromatography, a term derived from the Greek words chroma, colour, and graphien, to record, was introduced by the Russian botanist Michael Tswett in 1906. He described the separation of a mixture of leaf pigments on a column of calcium carbonate.

CHROMATOGRAPHIC METHODS

In all the chromatographic techniques, difference in affinity involves the process of adsorption, or partition. In adsorption, the binding of a compound, to the surface of the solid phase takes place. In partition the relative solubility of a compound in two phases, results in the partition of the compound in two phases.

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